1. Field of the Invention
The present invention relates to an image processing method for rotation or size change of an image and an apparatus therefor.
2. Related Background Art
In a conventional apparatus for rotation, enlargement or reduction of a digital image, such process has been conducted after input image data are once stored in a memory. The amount of information of the input image is generally larger than the corresponding amount processed image data, so that storage of the former requires a larger memory than the storage of the latter. Consequently the method of storing the input image information in a memory is inferior, in terms of memory cost and magnitude of circuitry, to a method of processing the input data in synchronization with a synchronization signal and storing the processed data in succession in an output memory.
On the other hand, the method of processing the input image data in consecutive manner for image rotation, enlargement or reduction in synchronization with a synchronization signal has a drawback of image quality deterioration because the processed data are sometimes not synchronized with the desired pitch of output signals, resulting in missing image data or in a misalignment of the image. FIGS. 1A and 1B illustrate such an example, wherein FIG. 1A shows the pitch of an original image, while, in FIG. 1B, broken lines indicate the pitch of an output image and solid lines indicate the pitch of an image obtained by a rotation of 35.degree. of the original image. Each rectangle corresponds to a pixel, and the value of each pixel of the rotated image is given to an output pixel, or broken-lined rectangle, in which the center of said rotated image pixel is positioned. In such image processing, the hatched output pixels become missing pixels, i.e., pixels to which no corresponding image data is assigned. FIG. 1C shows similar missing pixels in an image processing of a rotation of 38.degree. combined with image size variations of 80% in the main scanning direction and 120% in the sub scanning direction.
Also in such conventional apparatus, for example in the case of an image rotation of 30.degree. as shown in FIG. 1D, the outputting of the processed result image is started from a pixel on a line 215 in the sub-scanning direction of the original image, and the addresses of pixels 212, 213 for starting the outputting of processed image are obtained by complicated calculations. Such method, when applied to an apparatus requiring a high image quality such as in a color image processing or a high speed, requires a long time, or requires a large amount of hardware for achieving such process, or eventually results in a deteriorated image quality.